The purpose of this request for competing continuation funding is to continue our work on dissecting and defining the fundamental nature of the host immune response in the lung after exposure of mice to a realistic low dose aerosol infection with Mycobacterium tuberculosis. While our past work has contributed significantly to the definition of the acquired response, it is now clear that early resistance in the lung to infection is regulated by potentially redundant layers of very poorly understood innate immune mechanisms in addition to the better-characterized TH1 protective response. In the next funding period we propose a series of experiments to define these early mechanisms more clearly using a variety of approaches including flow cytometry, high speed fluorescence-activated cell sorting, histology, and immunohistochemistry. In our first Aim we will continue to try to identify sources of IFN-gamma that appear very early during the course of the infection, concentrating on the role of NK/NKT cell subsets and their potential restriction by Class-Ib MHC encoded molecules. In a second Aim, we propose to continue studies that are constructed to define the basic requirements needed to adequately and efficiently focus lymphocytes into the infected lungs, using a combination of flow cytometric analysis and sorting followed by adoptive transfer of tagged specific T cell subsets and subsequent tracking. Finally, we propose a fresh look at the memory T cell response in tuberculosis, specifically concentrating on parameters such as longevity, turnover, and potential cell surface marker reversion, primarily defined by flow cytometry. The proposed work will draw upon the broad expertise of various members of the Mycobacteria Research Laboratories at Colorado State University, as well as several eminent consultants and advisers.